Moving retryable-err checks to errors.As, moving some to not-retryable

[Groxx]

Part 1 of 2 for solving retry storms, particularly around incorrectly-categorized errors (e.g. limit exceeded) and service-busy.

This PR moves us to errors.As to support wrapped errors in the future, and re-categorizes some incorrectly-retried errors. This is both useful on its own, and helps make #1174 a smaller and clearer change.

Service-busy behavior is actually changed in #1174, this PR intentionally maintains its current (flawed) behavior.

Commits are ordered for ease of reading / verifying, and the added tests pass at each stage (but I did not run the full suite each time):

• just adds test
• just moves to errors.As, tests still pass
• changes which types are retried
• (minor test fix)
• changes from feedback

[coveralls]

Pull Request Test Coverage Report for Build 0181880b-5443-4634-9400-8e5f001cb004

• 43 of 43 (100.0%) changed or added relevant lines in 1 file are covered.
• 11 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 63.851%

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Files with Coverage Reduction	New Missed Lines	%
internal/compatibility/thrift/history.go	11	57.65%
<!--	Total:	11		-->

Totals
Change from base Build 01816e39-350f-43ae-a79e-40eaad99261d:	0.1%
Covered Lines:	12433
Relevant Lines:	19472

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💛 - Coveralls